Exxon Mobil Corp. continued a year-long buying spree for U.S. natural-gas assets, paying $575 million for wells and reserves in Arkansas.

Thursday's deal with Petrohawk Energy Corp. underscores Exxon's continuing interest in acquiring gas in the U.S., despite low prices for the relatively clean-burning fuel used to heat homes and generate electricity.

Exxon became the largest gas producer in the U.S. after it bought XTO Energy Inc. in June for $25 billion. In July, Exxon paid $695 million for Denver-based Ellora Energy Inc.

Exxon said it produced 3.726 billion cubic feet of natural gas a day in the U.S. in the third quarter, about 16% of the nation's total consumption. The Petrohawk deal will add another 98 million cubic feet of daily production, according to analysts at Jefferies & Co. The Ellora deal gave Exxon additional acreage in the prolific Haynesville shale, which straddles northern Louisiana and eastern Texas. Shale fields have reinvigorated U.S. natural-gas production in recent years.

Most U.S. gas producers are seeking to increase oil production to capitalize on high prices for crude, especially in comparison with natural gas. While oil prices have been climbing, closing above $90 a barrel on Wednesday, natural gas has been trading around $4 per million British thermal units, far below the $13 fetched in 2008. Petrohawk said early this month that it was considering selling assets to fund drilling activity in areas such as the oil-rich Eagle Ford shale in south Texas.

But the purchase by Exxon's XTO Energy unit of Petrohawk's holdings in the Fayetteville shale in Arkansas, shows that Exxon is bullish about the long-term prospects for natural gas. The Irving, Texas, company says gas will be the fastest-growing fuel through 2030.

The Petrohawk deal "provides a strategic addition to XTO's existing 410,000 net acre position in the Fayetteville shale trend," said Jeffrey Neu, an XTO spokesman. He said XTO will continue pursuing similar opportunities aimed at increasing domestic natural-gas output.

XTO also acquired Houston-based Petrohawk's pipeline assets in the Fayetteville Shale for $75 million.

The deal "looks like a good addition" to Exxon's existing shale-gas assets, according to analysts at Simmons & Co. The purchase also proves that XTO "can execute transactions well after the megamerger" with Exxon Mobil, Simmons said.

Exxon Mobil has said it intends to keep XTO's independence, deploying its expertise in shale-gas drilling across Exxon's global empire. Exxon is developing international shale-gas assets in Canada and Europe.